The subject invention is directed toward the valve art and, more particularly, to an improved stem tip seal structure.
The invention is especially suited for use in a particular diaphragm type shut-off valve and will be described with reference thereto; however, it will be appreciated that the invention is capable of broader application and could be used in a variety of different valves.
Typically, shut-off valves employ a valve member having a relatively soft, resilient material mounted on the end of the valve stem for sealing cooperation with a metal valve seat. A variety of different resilient materials mounted to the stem in different ways have been used in the prior art. While many of the prior art proposals have performed adequtely, seal breakdown, blowout, and chipping and nibbling have been ongoing problems. In addition, certain materials having highly desirably properties, such as high lubricity and resistance to attack by chemicals and high temperature, often produce cold flow and extrusion problems when used as stem tips seals.
Accordingly, there has been an ongoing need for a stem tip seal arrangement which overcomes the noted problems while allowing a variety of seal materials to be used safely and effectively.